AP Physics Multiple Choice Practice – Torque



AP Physics Multiple Choice Practice – Work-Energy

1. A mass m attached to a horizontal massless spring with spring constant k, is set into simple harmonic motion. Its maximum displacement from its equilibrium position is A. What is the masses speed as it passes through its equilibrium position?

[pic] B

2. A force F at an angle θ above the horizontal is used to pull a heavy suitcase of weight mg a distance d along a level floor at constant velocity. The coefficient of friction between the floor and the suitcase is µ. The work done by the frictional force is:

(A) –Fd cos θ (B) mgh – Fd cos θ (C) – µ Fd cos θ (D) -µmgd (E) -µ mgd cos θ

3. If the unit for force is F, the unit for velocity V, and the unit for time T, then the unit for energy is:

(A) FVT (B) F/T (C) FV/T (D) F/T2 (E) FV2/T2

4. A force of 10 N stretches a spring that has a spring constant of 20 N/m. The potential energy stored in the spring is:

(A) 2.5 J (B) 5.0 J (C) 10 J (D) 40 J (E) 200 J

5. A 2 kg ball is attached to a 0.80 m string and whirled in a horizontal circle at a constant speed of 6 m/s. The work done on the ball during each revolution is:

(A) 450 J (B) 90 J (C) 72 J (D) 16 J (E) zero

6. A pendulum bob of mass m on a cord of length L is pulled sideways until the cord makes an angle θ with the vertical as shown in the figure to the right. The change in potential energy of the bob during the displacement is:

(A) mgL (1–cos θ) (B) mgL (1–sin θ) (C) mgL sin θ

(D) mgL cos θ (E) 2mgL (1–sin θ)

7. A force F directed at an angle θ above the horizontal is used to pull a crate a distance D across a level floor. The work done by the force F is

(A) FD (B) FD cos θ (C) FD sin θ (D) mg sin θ (E) mgD cos θ

8. A compressed spring has 16 J of potential energy. What is the maximum speed it can impart to a 2 kg object?

(A) 2.8 m/s (B) 4.0 m/s (C) 5.6 m/s (D) 8.0 m/s (E) 16 m/s

9. A softball player catches a ball of mass m, which is moving towards her with horizontal speed V. While bringing the ball to rest, her hand moved back a distance d. Assuming constant deceleration, the horizontal force exerted on the ball by the hand is

(A) mV2/(2d) (B) mV2/d (C) mVd (D) 2mV/d (E) mV/d

10. A 3 kg block with initial speed 4 m/s slides across a rough horizontal floor before coming to rest. The frictional force acting on the block is 3 N. How far does the block slide before coming to rest?

(A) 1.0 m (B) 2.0 m (C) 4.0 m (D) 8.0 m (E) 16 m

11. A construction laborer holds a 20 kg sheet of wallboard 3 m above the floor for 4 seconds. During these 4 seconds how much power was expended on the wallboard?

(A) 2400 W (B) 340 W (C) 27 W (D) 15 W (E) none of these

12. A pendulum is pulled to one side and released. It swings freely to the opposite side and stops. Which of the following might best represent graphs of kinetic energy (Ek), potential energy (Ep) and total mechanical energy (ET)

[pic]

C

Problems 13 and 14 refer to the following situation: A car of mass m slides across a patch of ice at a speed v with its brakes locked. It the hits dry pavement and skids to a stop in a distance d. The coefficient of kinetic friction between the tires and the dry road is µ.

13. If the car has a mass of 2m, it would have skidded a distance of

(A) 0.5 d (B) d (C) 1.41 d (D) 2d (E) 4 d

14. If the car has a speed of 2v, it would have skidded a distance of

(A) 0.5 d (B) d (C) 1.41 d (D) 2d (E) 4 d

15. A ball is thrown vertically upwards with a velocity v and an initial kinetic energy Ek. When half way to the top of its flight, it has a velocity and kinetic energy respectively of

[pic]

16. A football is kicked off the ground a distance of 50 yards downfield. Neglecting air resistance, which of the following statements would be INCORRECT when the football reaches the highest point?

(A) all of the balls original kinetic energy has been changed into potential energy

(B) the balls horizontal velocity is the same as when it left the kickers foot

(C) the ball will have been in the air one-half of its total flight time

(D) the ball has an acceleration of g

(E) the vertical component of the velocity is equal to zero

17. A mass m is attached to a spring with a spring constant k. If the mass is set into motion by a displacement d from its equilibrium position, what would be the speed, v, of the mass when it returns to equilibrium position?

[pic]

18. If M represents units of mass, L represents units of length, and T represents units of time, the dimensions of power would be:

[pic]

19. An automobile engine delivers 24000 watts of power to a car’s driving wheels. If the car maintains a constant speed of 30 m/s, what is the magnitude of the retarding force acting on the car?

(A) 800 N (B) 960 N (C) 1950 N (D) 720,000 N (E) 1,560,000 N

20. A fan blows the air and gives it kinetic energy. An hour after the fan has been turned off, what has happened to the kinetic energy of the air?

(A) it disappears (B) it turns into potential energy (C) it turns into thermal energy

(D) it turns into sound energy (E) it turns into electrical energy

21. A box of old textbooks is on the middle shelf in the bookroom 1.3 m from the floor. If the janitor relocates the box to a shelf that is 2.6 m from the floor, how much work does he do on the box? The box has a mass of 10 kg.

(A) 13 J (B) 26 J (C) 52 J (D) 130 J (E) 260 J

22. A mass, M, is at rest on a frictionless surface, connected to an ideal horizontal spring that is unstretched. A person extends the spring 30 cm from equilibrium and holds it by applying a 10 N force. The spring is brought back to equilibrium and the mass connected to it is now doubled to 2M. If the spring is extended back 30 cm from equilibrium, what is the necessary force applied by the person to hold the mass stationary there?

(A) 20 N (B) 14.1 N (C) 10 N (D) 7.07 N (E) 5 N

1. 23. A deliveryman moves 10 cartons from the sidewalk, along a 10-meter ramp to a loading dock, which is 1.5 meters above the sidewalk. If each carton has a mass of 25 kg, what is the total work done by the deliveryman on the cartons to move them to the loading dock?

(A) 2500 J (B) 3750 J (C) 10000 J (D) 25000 J (E) 37500 J

1. 24. A rock is dropped from the top of a tall tower. Half a second later another rock, twice as massive as the first, is dropped. Ignoring air resistance,

1. (A) the distance between the rocks increases while both are falling.

2. (B) the acceleration is greater for the more massive rock.

3. (C) the speed of both rocks is constant while they fall.

4. (D) they strike the ground more than half a second apart.

5. (E) they strike the ground with the same kinetic energy.

2.

3. 25. A 60.0-kg ball of clay is tossed vertically in the air with an initial speed of 4.60 m/s. Ignoring air resistance, what is the change in its potential energy when it reaches its highest point?

4. (A) 0 J (B) 45 J (C) 280 J (D) 635 J (E) 2700 J

26. Which of the following is true for a system consisting of a mass oscillating on the end of an ideal spring?

(A) The kinetic and potential energies are equal to each other at all times.

(B) The kinetic and potential energies are both constant.

(C) The maximum potential energy is achieved when the mass passes through its equilibrium position.

(D) The maximum kinetic energy and maximum potential energy are equal, but occur at different times.

(E) The maximum kinetic energy occurs at maximum displacement of the mass from its equilibrium position

27. From the top of a high cliff, a ball is thrown horizontally with initial speed vo. Which of the following graphs best represents the ball's kinetic energy K as a function of time t ?

[pic] [pic] [pic] E

28. A person pushes a box across a horizontal surface at a constant speed of 0.5 meter per second. The box has a mass of 40 kilograms, and the coefficient of sliding friction is 0.25. The power supplied to the box by the person is (A) 0.2 W (B) 5 W (C) 50 W (D) 100 W (E) 200 W

29. A horizontal force F is used to pull a 5-kilogram block across a floor at a constant speed of 3 meters per second. The frictional force between the block and the floor is 10 newtons. The work done by the force F in 1 minute is most nearly

(A) 0 J (B) 30 J (C) 600 J (D) 1,350 J (E) 1,800 J

Questions 30-31: A block oscillates without friction on the end of a spring as shown. The minimum and maximum lengths of the spring as it oscillates are, respectively, xmin and xmax. The graphs below can represent quantities associated with the oscillation as functions of the length x of the spring.

30.Which graph can represent the total mechanical energy of the block-spring system as a function of x?

(A) A (B) B (C) C (D) D (E) E

31. Which graph can represent the kinetic energy of the block as a function of x?

(A) A (B) B (C) C (D) D (E) E

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